Process for Making a Layered Composite Structure

ABSTRACT

The invention relates to a process for the production of a layered composite structure comprising (1) a semi-permeable membrane made of a polymer composition comprising a polyetherester elastomer and (2) at least one web layer bonded to the membrane, wherein the process comprises a step wherein a melt layer of the polymer composition is applied onto the at least one web layer, and wherein the polyetherester elastomer comprises polyether soft segments formed from poly(alkylene-ether)glycols comprising alkylene-ether segments formed from ethylene oxide and polyester hard segments consisting of ester units derivable from short chain diols and dicarboxylic acid consisting of 98-65 mole % terephthalic acid (TPA), 2-35 mole % isophthalic acid (IPA) and optionally 0-20 mole % other dicarboxylic acids, wherein the mole % is relative to the total molar amount of dicarboxylic acid.

The invention relates to a process for the production of a layeredcomposite structure as well as to a layered composite structurecomprising (1) a semi-permeable membrane made of a polymer compositioncomprising a polyetherester elastomer and (2) at least one web layerbonded to the membrane.

Such a layered composite structure is known from EP-0708212-B1. In theknown layered composite structure of EP-0708212-B1, a barrier layerconsisting of a polyetherester elastomer (TPE-E) film is bonded to twonon-woven layers made of polyester fibers, one non-woven layer at eachside of the film. The said two non-woven layers and the barrier layerare bonded to each other with a water and water-vapour resistantadhesive. This bonding technique will be referred in this description as“lamination”. The barrier layer is said to be water-swellable, permeableto water-vapour and impermeable to water. In this application such abarrier layer and a semi-permeable membrane are considered to beequivalent. The TPE-E in the known layered composite structure is Hytrel8206 HTR from the company DuPont, which is a TPE-E type block copolymerswith EO/PO soft blocks and hard blocks composed of polyester segmentsderived from terephthalic acid and butanediol, also known aspolybutylene terephtalate (PBT) hard blocks.

In the same patent EP-0708212-B1 also a layered composite structure isdescribed which is made by “Aufextrudieren”, in other words “extrusioncoating”, which corresponds in general terms with a melt process. Thepolymer that is used in said process for making the barrier layer is athermoplastic polyurethane or a polyetherpolyamide block-copolymer(TPE-A). In the extrusion coating process, described in EP-0708212-B1,the polymer is extruded onto one web layer and than the second web layeris pressed onto the other side of the polymer layer.

Melt processes in general and extrusion coating in particular areconsidered economically more favorable than lamination, since meltprocesses effectively combine production of the barrier layer andbonding of the barrier layer to one or two web layers in one step.Extrusion is particularly preferred for formation of “endless” products,i.e. for products which emerge at continuous length. It has beenobserved by the inventors, however, that if the extrusion process isapplied with a water-swellable TPE-E like the one that is described inEP-0708212-B1, i.e. a TPE-E with PBT hard blocks and with EO/PO softblocks, a number of problems occur. One of the problems is that theadhesion of the barrier layer to the web layers is insufficient. Thisbecomes evident in particular when the layered composite structure issubjected to moisture and when the web layer or layers are made of anapolar material such as polyolefines. Already under dry conditions theadhesion is weak and as a result of swelling of the barrier layer underwet conditions extensive local debonding of the barrier layer and theweb layers occur.

More or less the same problem has been described in EP-0708212-B1 tooccur after swelling for a layered composite structure comprising abarrier layer comprising a hydrophilic water-swellable TPE-E bonded toone web layer. This problem is solved in EP-0708212-B1 with a layeredcomposite structure with two web layers bonded to the barrier layer.This might likewise work for a lamination process wherein a waterresistant adhesive is used in combination with a barrier layer made ofthe said TPE-E, but apparently is does not for a melt process likeextrusion coating.

A further disadvantage of the known layered composite structurecomprising a barrier layer comprising a hydrophilic water-swellableTPE-E is that the water resistant adhesive can reduce the water-vapourpermeability of the membrane.

The aim of the invention is therefore to provide a melt process formaking a layered composite structure with a semi-permeable membrane madeof a hydrophilic TPE-E that does not have the problems of the knownprocess, or at least so in a lesser extent.

This aim has been achieved with the process according to the invention,wherein a melt layer of a polymer composition comprising apolyetherester elastomer is applied onto at least one web layer, andwherein the polyetherester elastomer (TPE-E) comprises:

-   -   polyether soft segments formed from poly(alkylene-ether)glycols        comprising alkylene-ether segments formed from ethylene oxide        and    -   polyester hard segments consisting of ester units derivable from        short chain diols and dicarboxylic acid consisting of 98-65 mole        % terephthalic acid (TPA) and 2-35 mole % isophthalic acid (IPA)        and 0-20 mole % other dicarboxylic acids, or alkyl ester        derivatives of the carboxylic acids, the mole % relative to the        total molar amount of dicarboxylic acid.

The effect of the use of the said TPE-E in the process according to theinvention is that a better adhesion is obtained between the barrierlayer and the web layer or layers in both dry and wet conditions,compared to the corresponding process wherein a TPE-E polyester is usedwith hard segments consisting of ester units derivable from short chaindiols and dicarboxylic acid, or a alkyl ester derivative thereof,consisting of 100 mole % terephthalic acid (TPA). A further advantage isthat since no separate water resistant adhesive has to be used to obtaingood adhesion; the negative effect thereof on the water vapourpermeability properties of the membrane can thus be eliminated.

This effect of improved adhesion is surprising in view of the followingobservations by the inventors: the melt process described above is knownto be already commercially applied for the production of layeredcomposite structures making use of a polymer composition comprising apolyetherester elastomer based on polybutylene terephtalate (PBT) hardblocks and polytetramethylene glycol soft blocks. This process resultsin layered composite structures with a good adhesion between the polymerlayer and the membrane layer or layers. This TPE-E however, is fairlyhydrophobic and practically non-swelling. In the experiments executed bythe inventors wherein the polytetramethylene glycol soft blocks arereplaced by the more hydrophilic poly(alkylene-ether)glycols comprisingalkylene-ether segments formed from ethylene oxide in order to make thepolymer film more permeable to water vapour, the adhesion deterioratedseverely as according to the results described above. In an attempt toreach a compromise between the water vapour permeability and adhesionproperties, additional experiments were performed with a mixture of twoTPE-E's: one TPE-E with soft blocks based on thepoly(alkylene-ether)glycols comprising alkylene-ether segments formedfrom ethylene oxide and the other TPE-E comprising thepolytetramethylene glycol soft blocks. However, even with a very largecontent of the second TPE-E no significant improvement in adhesion wasobserved.

The polyetherester elastomer (TPE-E) that is used in the processaccording to the invention comprises polyether soft segments formed frompoly(alkylene-ether)glycols comprising alkylene-ether segments formedfrom ethylene oxide and polyester hard segments consisting of esterunits derivable from short chain diols and dicarboxylic acid consistingof 98-65 mole % terephthalic acid (TPA) and 2-35 mole % isophthalic acid(IPA).

Such polyetherester elastomers are known per se, and described forexample in U.S. Pat. No. 5,116,937. This patent mentions that theseelastomers can be used in fibres, films and moulded articles, butrelates in particular to artificial fishing lures. The patent does notrelate to a process for producing a layered composite structure and doesneither disclose nor suggest the advantageous effect thereof asaccording to the present invention.

Poly(alkylene ether)glycols from which the soft segments in the TPE-Eare formed may have a molecular weight varying over a wide range.Preferably the poly(alkylene ether)glycol has a weight average molecularweight (Mw) in the range of about 500 to about 6000, more preferably2000-4500. Also the content of alkylene-ether segments formed fromethylene oxide may vary over a wide range, typically 5-100 wt. %,relative to the weight of the poly(alkylene-ether)glycol. Preferably,the poly(alkylene ether)glycol comprises at least 30 wt. %, morepreferably at least 50 wt. %, alkylene-ether segments formed fromethylene oxide, wherein the wt % is relative to the weight of thepoly(alkylene-ether)glycol. The advantage of a higher ethylene oxide wt.% is that the membrane in the resulting layered composite constructionhas a higher water vapour permeability.

Specific examples of poly(alkylene ether)glycols comprisingalkylene-ether segments formed from ethylene oxide useful in the TPE-Einclude poly(ethyleneoxide)glycol also known as poly(ethylene glycol),copolymers of ethylene glycol and other glycols like 1,3-propyleneglycol and 1,4-butylene glycol, block-copolymers of poly(ethyleneglycol) and other poly(alkylene-ether)glycols like poly(1,3-propyleneglycol), poly(1,4-butylene glycol), poly(tetrahydrofuran),poly(pentamethylene glycol), poly(hexamethylene glycol), andpoly(hepthamethylene glycol), and bishydroxyphenyl ethoxylates like4,4′-isopropylidenediphenol ethoxylate (Bisphenol A ethoxylate), and4,4′-(1-phenylethylidene)bisphenol ethoxylate (Bisphenol AP ethoxylate),and mixtures derived thereof. An example of a suitable block-copolymerof poly(ethylene glycol) is poly(propylene-ether)glycol end-capped withpoly(ethylene-ether) segments, also known as EO/PO block copolymer.Preferably, the polyether soft segments are formed from apoly(ethylene-oxide)glycol or from a EO/PO block copolymer consisting ofa poly(propylene-ether)glycol end-capped with poly(ethylene-ether)segments.

Next to the poly(alkylene ether)glycols comprising alkylene-ethersegments formed from ethylene oxide, the TPE-E may comprise softsegments derived from other poly(alkylene ether)glycols, for example,poly(propylene)glycol and poly(tetramethylene)glycol. Preferably, thecontent of the other poly(alkylene ether)glycols is such that content ofalkylene-ether segments formed from ethylene oxide in the TPE-E is atleast 30 wt. %, more preferably at least 50 wt. %, relative to the totalweight of the poly(alkylene-ether)glycol. Also preferably, the TPE-Edoes not comprise such other poly(alkylene ether)glycols at all.

Short chain diols useful in the TPE-E include non-substituted,substituted, straight chain, branched, cyclic aliphatic,aliphatic-aromatic and aromatic diols having from 2 carbon atoms to 36carbon atoms. Specific examples of the desirable short chain diolinclude ethylene glycol, propylene glycol, 1,3-propanediol,1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol,1,12-dodecanediol, 1,14-tetradecanediol, 1,16-hexadecanediol,4,8-bis(hydroxymethyl)-tricyclo[5.2.1.0/2.6]decane,1,4-cyclohexanedimethanol, isosorbide, di(ethylene glycol), tri(ethyleneglycol) and mixtures derived therefrom. Essentially any glycol known canbe used. Preferably, the short chain diols are selected from the groupconsisting of ethylene glycol, propylene glycol, 1,3-propanediol,1,4-butanediol and mixtures thereof, more preferably the short chaindiols consist of ethylene glycol and/or 1,4-butanediol. The advantage ofthe preferred diols is that the membrane better retains its consistencyand mechanical properties at elevated temperature.

The dicarboxylic acid components from which the TPE-E used in thisinvention can be made, may comprise, apart from terephthalic acid (TPA)and isophthalic acid (IPA), up to and including 20 mole %, preferably atmost 10 mole %, or at most 5 mole % other dicarboxylic acids. Suitableother dicarboxylic acids include aromatic dicarboxylic acids likenaphthanates and bibenzoates, and aliphatic dicarboxylic acids, likeoxalic acid, malonic acid, succinic acid, and mixtures thereof.

For the preparation of these polyetherester elastomer, instead of thedicarboxylic acids, also use can be made of an ester derivative thereof,such as dimethyl terephthalate (DMT) and dimethyl isophthalate (DMI).

In a preferred embodiment, the dicarboxylic acid components don'tcomprise other dicarboxylic acids and consist of 95-65 mole % TPA and5-25 mole % IPA, more preferably 90-80 mole % TPA and 10-20 mole % IPA,or an ester derivative thereof.

The TPE-E that is used in the present invention may also comprising apolyfunctional branching agent. Polyfunctional branching agents that canbe used in the TPE-E include any agents having three or more carboxylicacid functions, hydroxy functions or mixtures thereof. Branching agents,if any, are typically used in an amount of 0.01-2.0 mole %, morepreferably 0.1-1 mole %, relative to the total molar amount ofdicarboxylic acid.

In a preferred embodiment, the polyetherester elastomer that is used forthe production of the layered composite structure consists of

-   -   soft segments formed from a poly(ethylene-oxide)glycol or from a        EO/PO block copolymer consisting of a        poly(propylene-ether)glycol end-capped with poly(ethylene-ether)        segments,    -   hard segments consisting of ester units derivable from ethylene        glycol and/or butane diol as short chain diol and 95-65 mole %        TPA and 5-25 mole % IPA as dicarboxylic acid,    -   and optionally a branching agent.

The TPE-Es used in the process according to the invention can beprepared by conventional polycondensation techniques. Well known methodsinclude the reaction of diol monomers with acid chlorides. Suchprocedures are described, for example, by R. Storbeck, et al., in J.Appl. Polymer Science, Vol. 59, pp. 1199-1202 (1996). Other methodsinclude the melt polymerization method, wherein the dicarboxylic acidcomponent (as acid or as an ester derivative thereof, or as a mixturethereof, the short chain diol and the poly(alkylene-ether)glycol andoptionally the polyfunctional branching unit, are combined in thepresence of a catalyst and heated to a high enough temperature that themonomers combine to form esters and diesters, then oligomers, andfinally polymers.

The polymer composition that is used in the process according to theinvention for making the membrane layer can comprise, next to the TPE-E,additives known for use in polyetherester compositions. Such additivescan include thermal stabilizers such as, for example, phenolicantioxidants; secondary thermal stabilizers such as, for example,thioethers and phosphates; UV absorbers such as, for examplebenzophenone- and benzotriazole-derivatives; and/or UV stabilizers suchas, for example, hindered amine light stabilizers, (HALS) and carbonblack. Other additives that can be used include plasticizers, processingaids, flow enhancing additives, lubricants, pigments, flame retardants,impact modifiers, nucleating agents to increase crystallinity,antiblocking agents such as silica, and base buffers such as sodiumacetate, potassium acetate, and tetramethyl ammonium hydroxide.

The polymer composition can also comprise inorganic, organic and/orfillers, such as, for example, talc, mica, wollastonite,montmorillonite, chalk, diatomaceous earth. Preferably clay fillers areused which can exfoliate to provide nanocomposites. This is especiallytrue for the layered silicate clays, such as smectite clays, magnesiumaluminum silicate, bentonite clays, montmorillonite clays, and hectoriteclays. Such clays can be natural or synthetic, treated or not. Theparticle sizes of fillers for use in the polymer composition can bewithin a wide range. As known to those skilled in the art, the fillerparticle size can be tailored based on the desired use of the layeredcomposite structure comprising the semi-permeable membrane. It is,generally preferred that the average diameter of the filler be less thanabout 40 microns. More preferably, the average diameter of the filler isless than about 20 microns. However, fillers having diameters outsidethe preferred ranges can be used. The filler can include particle sizesranging up to 40 mesh, (US Standard), or larger. Mixtures of fillerparticle sizes can also be advantageously used.

The web layer that can be used in the process according to the inventioncan be any web layer that is suitable as a substrate or support layerfor the semi-permeable membrane. Such web layers are preferably waterand water vapour resistant, light weight and tear resistant. The weblayer may be either of both woven and non-woven. Also combinations ofdifferent types of web layers can be used. These web layers can beproduced by known methods from both natural and industrial materials.

Preferably, the web layers comprise, or consist of, fibres made of apolyolefine, like polyethylene and polypropylene, polyester or otherthermoplastic polymer. Preferably, the at least one web layer that isused in the process according to the invention is a woven or non-wovenfibrous layer comprising polyolefine fibres. The advantage is that withpolyolefine fibres the largest improvement in adhesion is obtained.

For the application of the polymer melt onto the at least one web layer,any process that is suitable for applying a polymer melt layer may beused. Suitable processes are, for example, extrusion coating andcalendaring. In the process according to the invention, the polymer meltcan be applied to either one web layer or to two web layers. In theembodiment wherein the polymer melt is applied to two web layers, themelt may applied simultaneously to both web layers, for example, by meltextrusion in between the two web layers, or sequentially, for example byextrusion of the melt on one web layer and subsequently pressing thesecond web layer on the top surface of the melt. The two web layers thatare used in this process may be the same, but also a combination of twodifferent web layers may be used.

The thickness of the semi-permeable membrane layer in the layeredcomposite structure obtained by the process according to the inventionmay vary over a wide range, e.g. in the range of 5-500 μm. Preferably,the thickness lies in the range of 10-100 μm, more preferably 20-40 μm.

The invention also relates to the layered composite structure obtainablewith the process according to the invention, and any (preferred)embodiment thereof. The layered composite structure resulting from theprocess according to the invention may be a composite structure withonly one web layer bonded to one side of the membrane, or with two weblayers, one bonded at each side of the membrane.

The invention also relates to the use of the layered composite structureobtainable with the process according to the invention in building andconstruction applications. The advantage of the layered compositestructure according to the invention is the good adhesion even under wetconditions and the water vapour permeability combined with watertightness.

The invention is further elucidated with the following Examples andComparative Experiments.

Materials

For the experiments granulates of polyether ester compositions preparedfrom dimethyl terephthalate (DMT), dimethyl isophthalate (DMI), butanediol, and different polyols, were used. For the preparation industrialgrade materials were used. The compositions of the various polyetheresters used are indicated in Table I. For the polyols, the followingabbreviations are used: PEG 2000 (PEG with a Mn of about 2000 g/mol);PE-3500 (pEO/pPO/pEO triblock copolymer with a Mn of about 2200 g/moland 33 wt % pPO); PE-6200 (pEO/pPO/pEO triblock copolymer with a Mn ofabout 2200 g/mol and 67 wt % pPO); p-THF (polytetrahydrofurane, alsoindicated as polytetramethyleneglycol, with an Mn of about 2000).

Coating Experiments

The polyether ester granulates were fed into an extruder and extruded ata temperature of 250-255° C. through a slit dye and extrusion coatedinto the gap between co-rotating fleeces of non-woven polyolefinelayers, thus forming a construction of a polymer film with a thicknessof about 25 μm, sandwiched between the two non-woven polyolefine layers.

Adhesion Test

For the adhesion tests it was attempted to pull the two non-wovenpolyolefine layers apart. After separation the layers were inspection asto whether delamination of the layers has occurred due to cohesivefailure of the polymer film, as evidenced by rupture within the polymerfilm and retention of parts of the polymer film on both polyolefinelayers, adhesive failure between the polymer film and polyolefinelayers, as evidenced by separation of the polymer film from one or bothpolyolefine layers with absence of both rupture of the film and absenceof fiber pull out, or due to cohesive failure of polyolefine layers asevidenced from fiber pull out of one or both polyolefine layers. Thetest results have been collected in Table 1. No significant differenceshave been observed in the test results between tests performed on drysamples and tests performed on samples wetted by soaking andequilibrating for 24 hours in water.

TABLE 1 Polyetherester composition and adhesion test results forExamples I-III and Comparative Experiments A-F Ex. I Ex. II Ex. III CE-ACE-B CE-C CE-D CE-E CE-F Polymer composition Blend of 20 wt. % CE-D 80wt. % CE-F DMT (mole %) 85 85 85 100 100 100 100 100 DMI (mole %) 15 1515 0 0 0 0 0 Butane diol + + + + + + + + Polyol Type PEG2000 PE3500PE6200 PEG2000 PE3500 PE6200 PE6200 pTHF Amount Polyol (wt. %) 35 40 4035 40 40 55 60 Adhesion A-F A-F A-PF N N N N N A-F A-F = good adhesionwith extensive fibre pull out; A-PF = adhesion with partial fibre pullout; N = negative test result, no adhesion, absence of fiber pull out.

1. Process for the production of a layered composite structurecomprising (1) a semi-permeable membrane made of a polymer compositioncomprising a polyetherester elastomer and (2) at least one web layerbonded to the membrane, wherein the process comprises a step wherein amelt layer of the polymer composition is applied onto the at least oneweb layer, and wherein the polyetherester elastomer comprises polyethersoft segments formed from poly(alkylene-ether)glycols comprisingalkylene-ether segments formed from ethylene oxide and polyester hardsegments consisting of ester units derivable from short chain diols anddicarboxylic acid consisting of 98-65 mole % terephthalic acid (TPA),2-35 mole % isophthalic acid (IPA) and optionally 0-20 mole % otherdicarboxylic acids, wherein the mole % is relative to the total molaramount of dicarboxylic acid.
 2. Process according to claim 1, whereinthe polyether soft segments comprise at least 30 wt. % alkylene-ethersegments formed from ethylene oxide.
 3. Process according to claim 1,wherein the polyether soft segments are formed from apoly(ethylene-oxide)glycol or from a EO/PO block copolymer consisting ofa poly(propylene-ether)glycol end-capped with polyethylene-ether)segments.
 4. Process according to claim 1, wherein the short chain diolsare selected from the group consisting of ethylene glycol, propyleneglycol, 1,3-propanediol and 1,4-butandediol, and mixtures thereof. 5.Process according to claim 1, wherein the dicarboxylic acid consist of95-75 mole % TPA and 5-25 mole % IPA, preferably 90-80 mole % TPA and10-20 mole % IPA.
 6. Process according to claim 1, wherein the at leastone web layer is a woven or non woven fibrous layer comprisingpolyolefine fibres.
 7. Process according to claim 1, wherein the polymermelt is applied to two web layers and the layered composite structureresulting from the process comprises the membrane bonded to the two weblayers one at each side of the membrane.
 8. Layered composite structureobtainable with the process according to claim
 1. 9. Use of the layeredcomposite structure according to claim 8 in building and constructionapplications.